Protein skimmer



FIG. 1 is a front perspective view of the protein skimmer;

FIG. 2 is a rear perspective view of the protein skimmer;

FIG. 3 is a front view of the protein skimmer;

FIG. 4 is a rear view of the protein skimmer;

FIG. 5 is a right side view of the protein skimmer;

FIG. 6 is a left side view of the protein skimmer;

FIG. 7 is a top view of the protein skimmer; and,

FIG. 8 is a bottom view of the protein skimmer. 

The ornamental design for a protein skimmer, as shown and described. 